U.S. patent application number 13/596956 was filed with the patent office on 2013-02-28 for display apparatus using a backlight.
The applicant listed for this patent is Isao Matsuda, Yoshio Umeda, Akihiro YAMAMURA. Invention is credited to Isao Matsuda, Yoshio Umeda, Akihiro YAMAMURA.
Application Number | 20130049616 13/596956 |
Document ID | / |
Family ID | 47742668 |
Filed Date | 2013-02-28 |
United States Patent
Application |
20130049616 |
Kind Code |
A1 |
YAMAMURA; Akihiro ; et
al. |
February 28, 2013 |
DISPLAY APPARATUS USING A BACKLIGHT
Abstract
The instant application describes a display apparatus that
includes a display panel configured to display an image; and a
backlight unit configured to illuminate the display panel from a
back of the display panel. The backlight unit includes: N
light-emitting diode strings connected in parallel with each other,
each of the N light-emitting diode strings includes M
light-emitting diodes connected in series, N being an integer of 2
or more and M being an integer of 1 or more; a power source unit
connected in series with the N light-emitting diode strings and
configured to generate a voltage; a drive unit connected in series
with the N light-emitting diode strings and the power source unit
and configured to supply currents to the N light-emitting diode
strings; and a current regulator configured to regulate current
flowing in each of the N light-emitting diode strings.
Inventors: |
YAMAMURA; Akihiro; (Osaka,
JP) ; Matsuda; Isao; (Hyogo, JP) ; Umeda;
Yoshio; (Hyogo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
YAMAMURA; Akihiro
Matsuda; Isao
Umeda; Yoshio |
Osaka
Hyogo
Hyogo |
|
JP
JP
JP |
|
|
Family ID: |
47742668 |
Appl. No.: |
13/596956 |
Filed: |
August 28, 2012 |
Current U.S.
Class: |
315/192 |
Current CPC
Class: |
H05B 45/46 20200101 |
Class at
Publication: |
315/192 |
International
Class: |
H05B 37/02 20060101
H05B037/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2011 |
JP |
2011-186048 |
Claims
1. A display apparatus comprising: a display panel configured to
display an image; and a backlight unit configured to illuminate the
display panel from a back of the display panel, wherein the
backlight unit includes: N light-emitting diode strings connected
in parallel with each other, each of the N light-emitting diode
strings includes M light-emitting diodes connected in series, N
being an integer of 2 or more and M being an integer of 1 or more;
a power source unit connected in series with the N light-emitting
diode strings and configured to generate a voltage; a drive unit
connected in series with the N light-emitting diode strings and the
power source unit and configured to supply currents to the N
light-emitting diode strings; and a current regulator configured to
regulate current flowing in each of the N light-emitting diode
strings.
2. The display apparatus according to claim 1, wherein the current
regulator includes: a reference voltage generating circuit
configured to generate a reference voltage; a resistor element and
current regulating element connected in series with each of the N
light-emitting diode string; and a control circuit configured to
control the current regulating element based on the reference
voltage generated by the reference voltage generating circuit and a
detection voltage detected by the resistor element.
3. The display apparatus according to claim 2, wherein: the current
regulating element includes a transistor connected in series with
each of the N light-emitting diode strings, and the control circuit
includes an amplifier circuit configured to generate a voltage,
which controls the transistor, based on the reference voltage and
the detection voltage.
4. The display apparatus according to claim 3, wherein the
amplifier circuit includes a differential amplifier circuit.
5. The display apparatus according to claim 2, wherein: the current
regulating element includes a transistor connected in series with
each of the N light-emitting diode strings, and the control circuit
includes a Pulse Width Modulation (PWM) circuit configured to
output a PWM signal, which controls the transistor based on the
reference voltage and the detection voltage.
6. The display apparatus according to claim 3, wherein the
transistor includes a field-effect transistor.
7. The display apparatus according to claim 1, further comprising a
light emission controller configured to control, out of the N
light-emitting diode strings, K light-emitting diode strings to
which the currents are supplied simultaneously from the drive unit,
wherein: K is an integer of 2 or more but less than N, and the
current regulator is configured to regulate each current flowing in
each of the K light-emitting diode strings.
8. The display apparatus according to claim 1, further comprising a
light emission controller configured to perform a control so that
the current is supplied from the drive unit to each of the N
light-emitting diode strings sequentially and one by one, wherein
the current regulator is configured to regulate each current that
is supplied to each of the N light-emitting diode strings
sequentially and one by one by the light emission controller.
9. The display apparatus according to claim 7, wherein: the light
emission controller is configured to perform a control so that the
current is supplied from the drive unit to the one or each of the K
light-emitting diode strings at a predetermined period, and the
current regulator is configured to regulate each current supplied
to the one or each of the K light-emitting diode strings at the
predetermined period by the light emission controller.
10. The display apparatus according to claim 9, wherein: each of
the N light-emitting diode strings illuminates different regions of
the display panel, the N light-emitting diode strings include a
first light-emitting diode string and a second light-emitting diode
string, illuminating the regions adjacent to each other, and the
light emission controller is configured to perform a control so
that current is supplied from the drive unit to only the first
light-emitting diode string during a first period, that current is
supplied from the drive unit to each of the first and second
light-emitting diode strings during a second period subsequent to
the first period, and that current is supplied from the drive unit
to only the second light-emitting diode string during a third
period subsequent to the second period.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority to Japanese
Patent application No. 2011-186048 filed on Aug. 29, 2011, the
entire content of which is hereby incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present application relates to a display apparatus using
a backlight.
BACKGROUND
[0003] A display apparatus that has a display panel using a
non-self-emission type liquid crystal as a light modulation element
has a backlight unit for illuminating the display panel from the
back and displays an image by controlling the transmittance of the
light emitted from the backlight unit using the liquid crystal.
Light-emitting diodes and the like are used as light sources of the
backlight unit (see Japanese Patent Application Publication No.
2007-273204, for example).
[0004] However, the technology described in Japanese Patent
Application Publication No. 2007-273204 needs to measure the
resistance values of the light-emitting diodes and calculates the
average and standard deviation of the measured resistance values to
select the light-emitting diode having a desired resistance value.
This results in an increase in labor and costs for measuring a
resistance value, calculating the average and standard deviation,
selecting the light-emitting diode and the like.
[0005] To this end, there is a need for a display apparatus that is
capable of preventing or reducing variation in the light quantity
of light-emitting diodes, which is caused by fluctuations in
forward voltages of the light-emitting diodes, without increasing
labor and costs.
SUMMARY
[0006] In one general aspect, the instant application describes a
display apparatus that includes a display panel configured to
display an image; and a backlight unit configured to illuminate the
display panel from a back of the display panel. The backlight unit
includes: N light-emitting diode strings connected in parallel with
each other, each of the N light-emitting diode strings includes M
light-emitting diodes connected in series, N being an integer of 2
or more and M being an integer of 1 or more; a power source unit
connected in series with the N light-emitting diode strings and
configured to generate a voltage; a drive unit connected in series
with the N light-emitting diode strings and the power source unit
and configured to supply currents to the N light-emitting diode
strings; and a current regulator configured to regulate current
flowing in each of the N light-emitting diode strings.
[0007] The above general aspect may include one or more of the
following features. The current regulator may include a reference
voltage generating circuit configured to generate a reference
voltage; a resistor element and a current regulating element
connected in series with each of the N light-emitting diode string;
and a control circuit configured to control the current regulating
element based on the reference voltage generated by the reference
voltage generating circuit and a detection voltage detected by the
resistor element.
[0008] The current regulating element may include a transistor
connected in series with each of the N light-emitting diode
strings. The control circuit may include an amplifier circuit
configured to generate a voltage, which controls the transistor,
based on the reference voltage and the detection voltage. The
amplifier circuit may include a differential amplifier circuit.
[0009] The current regulating element may include a transistor
connected in series with each of the N light-emitting diode
strings. The control circuit may include a Pulse Width Modulation
(PWM) circuit configured to output a PWM signal, which controls the
transistor based on the reference voltage and the detection
voltage. The transistor may include a field-effect transistor.
[0010] The apparatus may further include a light emission
controller configured to control, out of the N light-emitting diode
strings, K light-emitting diode strings to which the currents are
supplied simultaneously from the drive unit. K may be an integer of
2 or more but less than N. The current regulator may be configured
to regulate each current flowing in each of the K light-emitting
diode strings.
[0011] The apparatus may further include a light emission
controller configured to perform a control so that the current is
supplied from the drive unit to each of the N light-emitting diode
strings sequentially and one by one. The current regulator may be
configured to regulate each current that is supplied to each of the
N light-emitting diode strings sequentially and one by one by the
light emission controller.
[0012] The light emission controller may be configured to perform a
control so that the current is supplied from the drive unit to the
one or each of the K light-emitting diode strings at a
predetermined period. The current regulator may be configured to
regulate each current supplied to the one or each of the K
light-emitting diode strings at the predetermined period by the
light emission controller.
[0013] Each of the N light-emitting diode strings may illuminate
different regions of the display panel. The N light-emitting diode
strings may include a first light-emitting diode string and a
second light-emitting diode string, illuminating the regions
adjacent to each other. The light emission controller may be
configured to perform a control so that current is supplied from
the drive unit to only the first light-emitting diode string during
a first period, that current is supplied from the drive unit to
each of the first and second light-emitting diode strings during a
second period subsequent to the first period, and that current is
supplied from the drive unit to only the second light-emitting
diode string during a third period subsequent to the second
period.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The figures depict one or more implementations in accordance
with the present teachings, by way of example only, not by way of
limitations. In the figures, like reference numerals refer to the
same or similar elements
[0015] FIG. 1 is a block diagram showing a configuration of an
exemplary liquid crystal display apparatus of the instant
application;
[0016] FIG. 2 is a circuit block diagram showing an example of a
circuit configuration of a backlight unit of the display apparatus
shown in FIG. 1;
[0017] FIG. 3 is a diagram schematically showing an example of an
arrangement of LED strings;
[0018] FIG. 4 is a timing chart showing an example of operations by
the LED strings in the configuration shown in FIG. 2;
[0019] FIG. 5 is a circuit block diagram showing another example of
the circuit configuration of the backlight unit;
[0020] FIG. 6 is a diagram schematically showing an example of an
arrangement of the LED strings in the circuit configuration shown
in FIG. 5;
[0021] FIG. 7 is a timing chart showing an example of operations by
the LED strings in the configuration shown in FIG. 5;
[0022] FIG. 8 is a timing chart showing another example of the
operations by the LED strings in the configuration shown in FIG.
5;
[0023] FIG. 9 is a circuit block diagram showing another example of
the circuit configuration of the backlight unit;
[0024] FIG. 10 is a timing chart showing an example of operations
by the LED strings in the configuration shown in FIG. 9;
[0025] FIG. 11 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit;
[0026] FIG. 12 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit;
[0027] FIG. 13 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit;
[0028] FIG. 14 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit;
[0029] FIG. 15 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit; and
[0030] FIG. 16 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit.
DETAILED DESCRIPTION
[0031] In the following detailed description, numerous specific
details are set forth by way of examples in order to provide a
thorough understanding of the relevant teachings. However, it
should be apparent to those skilled in the art that the present
teachings may be practiced without exemplary details. In other
instances, well known methods, procedures, components, and/or
circuitry have been described at a relatively high-level, without
detail, in order to avoid unnecessarily obscuring aspects of the
present concepts.
[0032] FIG. 1 is a block diagram showing a configuration of an
exemplary liquid crystal display apparatus of the instant
application. FIG. 2 is a circuit block diagram showing an example
of a circuit configuration of a backlight unit of the liquid
crystal display apparatus shown in FIG. 1.
[0033] The liquid crystal display apparatus shown in FIG. 1 has a
signal processor 1, a liquid crystal display panel 2, and a
backlight unit 3. The signal processor 1 generates a control signal
for controlling the liquid crystal display panel 2 and a control
signal for controlling the backlight unit 3 on the basis of an
input image signal from outside, and outputs the control signals
for controlling the liquid crystal display panel 2 to and the
control signal for controlling the backlight unit 3 to the
backlight unit 3. Although not shown, the liquid crystal display
panel 2 has a plurality of gate lines extending in a horizontal
direction, a plurality of source lines extending in a vertical
direction, a switching element, and a plurality of pixels, wherein
the plurality of pixels are disposed in the form of a matrix at the
intersections of the plurality of source lines with the plurality
of gate lines. An IPS (In Plane Switching) system, VA (Vertical
Alignment) system, or other drive systems may be employed as the
liquid crystal display panel 2. The IPS system, for example, is
employed in present implementation.
[0034] The backlight unit 3 illuminates the liquid crystal display
panel 2 from the back of the liquid crystal display panel 2. An
edge-type backlight system or direct-type backlight system may be
employed as an illumination system of the backlight unit 3. The
edge-type backlight system, for example, is employed in the present
implementation. The backlight unit 3 has light-emitting diode
strings (referred to as "LED strings" hereinafter) S11, S12, S21,
and S22, a power source unit 31, a drive unit 32, a current
regulator 33, and a light emission controller 34.
[0035] As shown in FIG. 2, the LED string S11 includes M white
light-emitting diodes L11, L12, . . . , L1M (e.g., M=10) connected
in series. Similarly, the LED string S12 includes M white
light-emitting diodes L21, L22, . . . L2M connected in series. The
LED string S21 includes M white light-emitting diodes L31, L32, . .
. L3M connected in series. The LED string S22 includes M white
light-emitting diodes L41, L42, . . . L4M connected in series. The
LED strings S11 and S12 constitute one group of light-emitting
diode strings. The LED strings S21 and S22 constitute another group
of light-emitting diode strings.
[0036] The power source unit (DC-DC converter) 31 generates a DC
voltage from an input voltage Vin to supply power to the LED
strings S11, S12, S21, and S22. The drive unit 32 supplies current
to the LED strings S11, S12, S21, and S22. The current regulator 33
regulates the current flowing in the LED strings S11, S12, S21, and
S22. The light emission controller 34 controls turning-on and
turning-off of the LED strings S11, S12, S21, and S22.
[0037] In the example of the circuit configuration shown in FIG. 2,
the drive unit 32 includes constant current sources 321 and 322.
The current regulator 33 includes differential amplifier circuits
331 to 334, a reference voltage generating circuit 335,
field-effect transistors 33A to 33D, and current sensing resistors
R11 to R14. The light emission controller 34 includes switch
controller 341 and transistors Q341 to Q344.
[0038] The DC-DC converter 31 is connected in series with the LED
strings S11, S12, S21, and S22. The reference voltage generating
circuit 335 generates a reference voltage Vref using the voltage
generated by the DC-DC converter 31. A drain and a source of the
field-effect transistor 33A and the current sensing resistor R11
are connected in series with the LED string S11. Similarly, a drain
and a source of the field-effect transistor 33B and the current
sensing resistor R12 are connected in series with the LED string
S12. The series circuit including the LED string S11, the
field-effect transistor 33A and the current sensing resistor R11,
and the series circuit including the LED string S12, the
field-effect transistor 33B and the current sensing resistor R12
are connected in parallel with each other. This parallel circuit is
connected in series between the DC-DC converter 31 and the constant
current source 321.
[0039] The differential amplifier circuits 331 and 332 are
connected to gates of the field-effect transistors 33A and 33B,
respectively. The collectors of the transistors Q341 and Q342 are
connected to the gates of the field-effect transistors 33A and 33B,
respectively. A switch controller 341 is connected to the base of
the transistor Q341. A switch controller 341 is connected to the
base of the transistor Q342. The emitters of the transistors Q341
and Q342 are grounded. For convenience of illustration, the switch
controller 341 is shown at four places in FIG. 2.
[0040] The differential amplifier circuit 331 has a two-input
one-output operational amplifier OA1 and resistors R1 to R4. A
non-inverting input terminal of the operational amplifier OA1 is
connected to a reference voltage output terminal of the reference
voltage generating circuit 335 via the resistor R1, and is grounded
via the resistor R2. An inverting input terminal of the operational
amplifier OA1 is connected to an end part of the current sensing
resistor R11 on the field-effect transistor 33A side via the
resistor R3, and is connected to an output terminal of the
operational amplifier OA1 via the resistor R4. The output terminal
of the operational amplifier OA1 is further connected to the gate
of the field-effect transistor 33A. Note that the differential
amplifier circuit 332 has the same configuration as the
differential amplifier circuit 331.
[0041] Peripheral circuits around the LED strings S21 and S22 are
also configured in the same manner as those around the LED strings
S11 and S12. In other words, the series circuit including the LED
string S21, the field-effect transistor 33C, and the current
sensing resistor R21, and the series circuit including the LED
string S22, the field-effect transistor 33D, and the current
sensing resistor R22 are connected in parallel with each other.
This parallel circuit is connected in series between the DC-DC
converter 31 and the constant current source 322. The other circuit
configurations are the same as those of the LED strings S11 and S12
described above. In the circuit configuration shown in FIG. 2, two
LED strings are connected in parallel with one constant current
source. However, the number of LED strings to be connected in
parallel is not necessarily limited to two and can be three or
more. Furthermore, the circuit configuration shown in FIG. 2 has
two constant current sources 321 and 322. However, the number of
constant current sources is not necessarily limited to two and can
be three or more.
[0042] Operations of the backlight unit 3 configured as described
above are now described. The LED strings S11 and S12 are connected
in parallel with the constant current source 321. In the circuit
configuration in which the parallel circuit of the LED strings S11
and S12 is simply connected to the constant current source 321,
when there are fluctuations in forward voltages Vf of the
light-emitting diodes L11 and L12 and the like configuring the LED
strings S11 and S12, respectively, the currents supplied by the
constant current source 321 do not flow evenly to the LED strings
S11 and S12, causing variations in the light quantity of the LED
strings S11 and S12.
[0043] In the configuration shown in FIG. 2, on the other hand, the
differential amplifier circuit 331 regulates a gate voltage of the
field-effect transistor 33A in accordance with a detection voltage
Vr11 of the current sensing resistor R11 and the reference voltage
Vref. In other words, when the Vr11 is greater than the Vref, the
differential amplifier circuit 331 reduces the gate voltage of the
field-effect transistor 33A. When the Vr11 is lower than the Vref,
on the other hand, the differential amplifier circuit 331 increases
the gate voltage of the field-effect transistor 33A. The
differential amplifier circuits 332, 333, and 334 are operated in
the same manner as the differential amplifier circuit 331.
Therefore, the differential amplifier circuits 331 to 334 regulate
the gate voltages of the field-effect transistors 33A to 33D
respectively, so that the detection voltages Vr11, Vr12, Vr21, and
Vr22 of the current sensing resistors R11, R12, R21, and R22 become
equal to one another as follows: Vr11=Vr12=Vr21=Vr22. As a result,
the currents flow evenly to the LED strings S11, S12, S21, and S22,
preventing or reducing the variations in the light quantity of the
light-emitting diodes L11 and the like.
[0044] According to the above-described implementation, the current
sensing resistor R11 and the field-effect transistor 33A are
connected in series with the LED string S11. The current sensing
resistor R12 and the field-effect transistor 33B are connected in
series with the LED string S12. The current sensing resistor R21
and the field-effect transistor 33C are connected in series with
the LED string S21. The current sensing resistor R22 and the
field-effect transistor 33D are connected in series with the LED
string S22. The differential amplifier circuits 331-334 regulate
the gate voltages of the field-effect transistors 33A-33D
respectively in accordance with the detection voltages of the
current sensing resistors and the reference voltage Vref. As a
result, the currents flow evenly to the LED strings S11, S12, S21,
and S22. Therefore, even when there are fluctuations in the forward
voltages of the light-emitting diodes L11 and the like, preventing
or reducing the variation in the light quantity of the
light-emitting diodes L11 and the like without increasing the labor
and costs.
[0045] The field-effect transistors 33A and 33B are connected in
series with the constant current source 321, and the field-effect
transistors 33C and 33D are connected in series with the constant
current source 322. Hence, withstand voltages of the constant
current sources 321 and 322 can be increased by the level of
withstand voltages of the field-effect transistors.
[0046] As described with reference to FIG. 2, in the present
implementation, the LED strings S11 and S12 are connected in
parallel with each other with respect to the constant current
source 321, and the LED strings S21 and S22 are connected in
parallel with each other with respect to the constant current
source 322. Next are described examples of specific operations that
are performed in such a configuration where the LED strings are
connected in parallel with each other with respect to the constant
current sources.
[0047] FIG. 3 is a diagram schematically showing an example of an
arrangement of the LED strings. FIG. 4 is a timing chart showing an
example of operations by the LED strings in the configuration shown
in FIG. 2. Section (A) of FIG. 4 shows current flowing in the LED
strings S11 and S21. Section (B) of FIG. 4 shows current flowing in
the LED strings S12 and S22.
[0048] As shown in FIG. 3, the LED string S11 is disposed in a left
half part of an upper end of the liquid crystal display panel 2.
The LED string S12 is disposed in a right half part of the upper
end of the liquid crystal display panel 2. The LED string S21 is
disposed in a left half part of a lower end of the liquid crystal
display panel 2. The LED string S22 is disposed in a right half
part of the lower end of the liquid crystal display panel 2.
[0049] In the present implementation, suppose that the constant
current sources 321 and 322 have a rated current of 120 mA. As
shown in FIG. 4, when steadily supplying current to each of the LED
strings, the constant current source 321 can supply current of 60
mA to the LED strings S11 and S12 because the LED strings S11 and
S12 are connected in parallel with each other with respect to the
constant current source 321. Similarly, the constant current source
322 can supply current of 60 mA to the LED strings S21 and S22
because the LED strings S21 and S22 are connected in parallel with
each other with respect to the constant current source 322. This
supply of current can illuminate the liquid crystal display panel 2
by means of the LED strings S11, S12, S21, and S22.
[0050] FIG. 5 is a circuit block diagram showing another example of
the circuit configuration of the backlight unit 3. FIG. 6 is a
diagram schematically showing an example of an arrangement of the
LED strings in the circuit configuration shown in FIG. 5. The
backlight unit 3 shown in FIG. 5 has one constant current source
321 and two LED strings S11 and S12. In the circuit configuration
shown in FIG. 5, the two LED strings S11 and S12 are connected in
parallel with the one constant current source 321. However, the
number of LED strings connected in parallel is not limited to two
and can be three or more. Further, the circuit configuration shown
in FIG. 5 has one constant current source 321. However, the number
of constant current sources is not limited to one and can be two or
more.
[0051] In the circuit configuration shown in FIG. 5, the drive unit
32 includes the constant current source 321. The current regulator
33 includes the differential amplifier circuits 331, 332, the
reference voltage generating circuit 335, the field-effect
transistors 33A and 33B, the current sensing resistors R11 and R12,
and the selector 336. Furthermore, the light emission controller 34
includes the switch controller 341 and the transistors Q341 and
Q342.
[0052] The reference voltage generating circuit 335 generates a
first reference voltage Vref1 and a second reference voltage Vref2.
Here, Vref1 may be greater than Vref2. The selector 336 outputs
either the first reference voltage Vref1 or the second reference
voltage Vref2 to the differential amplifier circuits 331 and 332 as
the reference voltage Vref of the differential amplifier circuits
331 and 332. The selector 336 is configured so as to be able to
output the same reference voltage or different reference voltages
to the differential amplifier circuits 331 and 332. Note that, for
convenience of illustration, the selector 336 is shown at two
places in FIG. 5.
[0053] As shown in FIG. 6, the LED string S11 is disposed in an
upper part of the liquid crystal display panel 2, and the LED
string S12 is disposed in a lower part of the liquid crystal
display panel 2.
[0054] FIG. 7 is a timing chart showing an example of operations by
the LED strings in the configuration shown in FIG. 5. Section (A)
of FIG. 7 shows a turning-on timing of an upper part of the liquid
crystal display panel 2. Section (B) of FIG. 7 shows a switch-on
timing of a lower part of the liquid crystal display panel 2.
Section (C) of FIG. 7 shows current flowing in the LED string S11.
Section (D) of FIG. 7 shows current flowing in the LED string S12.
Section (E) of FIG. 7 shows the reference voltage Vref of the
differential amplifier circuit 331 that is output from the selector
336. Section (F) of FIG. 7 shows the reference voltage Vref of the
differential amplifier circuit 332 that is output from the selector
336.
[0055] As shown in Sections (A) and (B) of FIG. 7, first, the upper
part of the liquid crystal display panel 2 is turned on during a
period T1. In the subsequent period T2, the lower part of the
liquid crystal display panel 2 is turned on, while the upper part
is kept turning on. In the subsequent period T3, the upper part of
the liquid crystal display panel 2 is turned off, but the lower
part remains turned on. Described next is the operations of the LED
strings that are performed when the on-duties of the upper part and
lower part of the liquid crystal display panel 2 overlap with each
other.
[0056] In the operations shown in FIG. 7, on-off of the LED string
S11 is achieved by on-off of the transistor Q341. In other words,
when the switch controller 341 outputs a high-level signal to the
base of the transistor Q341, the transistor Q341 is turned on. The
gate voltage of the field-effect transistor 33A drops, which turns
off the field-effect transistor 33A. As a result, the LED string
S11 is turned off. On the other hand, when the switch controller
341 outputs a low-level signal to the base of the transistor Q341,
the transistor Q341 is turned off. The gate voltage of the
field-effect transistor 33A reaches the value determined by the
differential amplifier circuit 331, which turns on the field-effect
transistor 33A. As a result, the LED string S11 is turned on. The
LED string S12 is turned on and off by the transistor Q342 in the
same manner.
[0057] First, when the period T1 starts, that is, when the upper
part of the liquid crystal display panel 2 is turned on, the
transistor Q341 is turned off, and, as shown in Section (E), the
first reference voltage Vref1 is output as the reference voltage
Vref, from the selector 336 to the differential amplifier circuit
331. Therefore, the differential amplifier circuit 331 regulates
the gate voltage of the field-effect transistor 33A in accordance
with the detection voltage Vr11 and the first reference voltage
Vref1. As a result, current of 120 mA is supplied to the LED string
S11, whereby the LED string S11 is turned on, as shown in Section
(C). At this moment, the transistor Q342 remains on, and no current
is supplied to the LED string S12. As a result, only the upper part
of the liquid crystal display panel 2 may be illuminated at
relatively high intensity.
[0058] At the time the subsequent period T2 is started, that is,
when the lower part of the liquid crystal display panel 2 is turned
on, the transistor Q342 is turned off, and, as shown in Section
(F), the second reference voltage Vref2 is output as the reference
voltage Vref, from the selector 336 to the differential amplifier
circuit 332. Therefore, the differential amplifier circuit 332
regulates the gate voltage of the field-effect transistor 33B in
accordance with the detection voltage Vr12 and the second reference
voltage Vref2. As a result, current of 60 mA is supplied to the LED
string S12, whereby the LED string S12 is turned on, as shown in
Section (F). At the same time, that is, when the period T2 is
started, the voltage that is output as the reference voltage Vref
from the selector 336 to the differential amplifier circuit 331 is
changed from the first reference voltage Vref1 to the second
reference voltage Vref2, while the transistor Q341 remains off, as
shown in Section (E). Therefore, the differential amplifier circuit
331 regulates the gate voltage of the field-effect transistor 33A
in accordance with the detection voltage Vr11 and the second
reference voltage Vref2. Consequently, current of 60 mA is supplied
to the LED string S11, as shown in Section (C). As a result, the
upper part and lower part of the liquid crystal display panel 2 are
illuminated at relatively low intensity.
[0059] At the time the subsequent period T3 is started, that is,
when the upper part of the liquid crystal display panel 2 is turned
off, the transistor Q341 is turned on. Consequently, as shown in
Section (C), the supply of current to the LED string S11 is
stopped. At the same time, that is, when the period T3 is started,
the voltage that is output as the reference voltage Vref from the
selector 336 to the differential amplifier circuit 332 is changed
from the second reference voltage Vref2 to the first reference
voltage Vref1, while the transistor Q342 remains off, as shown in
Section (F). Therefore, the differential amplifier circuit 332
regulates the gate voltage of the field-effect transistor 33B in
accordance with the detection voltage Vr12 and the first reference
voltage Vref1. Consequently, current of 120 mA is supplied to the
LED string S12, as shown in Section (D). As a result, only the
lower part of the liquid crystal display panel 2 may be illuminated
at relatively high intensity. At the end of the period T3, the
transistor Q342 is turned on, and the backlight unit 3 is turned
off. In the implementation shown in FIGS. 5 to 7, the period T1
corresponds to an example of a first period, the period T2
corresponds to an example of a second period, and the period T3
corresponds to an example of a third period.
[0060] As described above, in the implementation shown in FIGS. 5
to 7, the illuminated region on the liquid crystal display panel 2
changes from the upper part to the lower part from the period T1
through the period T3. However, with the period T2 during which the
upper part and lower part are illuminated with a small light
quantity, the transition of the illuminated region of the liquid
crystal display panel 2 can be made less noticeable. In addition,
in the implementation shown in FIGS. 5 to 7, because the
differential amplifier circuits 331 and 332 control the gate
voltages of the field-effect transistors 33A and 33B in two stages,
the light quantity of the LED strings S11 and S12 can also be
controlled in two stages. Therefore, the constant current source
321 does not have to be provided with current control function for
controlling the light quantity and the current flowing in the
constant current source 321 can be stabilized. Hence, the
configuration of the constant current source 321 can be simplified
as compared with the constant current source having the current
control function.
[0061] FIG. 8 is a timing chart showing another example of the
operations by the LED strings in the configuration shown in FIG. 5.
Section (A) of FIG. 8 shows current flowing in the LED string S11.
Section (B) of FIG. 8 shows current flowing in the LED string S12.
Section (C) of FIG. 8 shows on-off states of the transistor Q341.
Section (D) of FIG. 8 shows on-off states of the transistor
Q342.
[0062] Note that the LED strings S11 and S12 are disposed in a
manner shown in FIG. 6. In other words, the LED string S11 is
disposed in the upper part of the liquid crystal display panel 2,
whereas the LED string S12 is disposed in the lower part of the
liquid crystal display panel 2. Moreover, in the present
implementation, the constant current source 321 has a rated current
of 120 mA, as described above.
[0063] In the operations shown in FIG. 8, the LED strings are
turned on and off. As described above, the LED string S11 is turned
on and off by the on-off operations of the transistor Q341. The LED
string S12 is turned on and off by the on-off operations of the
transistor Q342. In the operations shown in FIG. 8, the voltages
that are output as the reference voltage Vref from the selector 336
to the differential amplifier circuits 331 and 332 include the
first reference voltage Vref1.
[0064] In the operations shown in FIG. 8, the LED strings S11 and
S12 that are connected in parallel with each other are turned on
and off alternately. In other words, the constant current source
321 supplies currents to the LED strings S11 and S12 alternately
and not simultaneously.
[0065] Therefore, as shown in Sections (A) and (B) of FIG. 8, the
constant current source 321 can supply current of 120 mA to the LED
string S11 and current of 120 mA to the LED string S12. As a
result, a cost increase that is caused by increasing the rated
current of the constant current source 321 can be prevented,
increasing the intensity of the light illuminating the liquid
crystal display panel 2.
[0066] In the circuit configuration shown in FIG. 5, while keeping
the transistors Q341 and Q342 off, the voltages that are output as
the reference voltage Vref from the selector 336 to the
differential amplifier circuits 331 and 332 are set at the second
reference voltage Vref2. Consequently, current of 60 mA can be
supplied to the LED strings S11 and S12 to continuously turning the
LED strings S11 and S12 on, as shown in FIG. 4. Further, as shown
in FIG. 8, when only the operation for alternately turning the LED
strings on and off is performed (i.e., when the operation for
continuously turning the LED strings on shown in FIG. 4 is not
performed), the reference voltage generating circuit 335 may be
configured to output the first reference voltage Vref1 as the
reference voltage Vref to the differential amplifier circuits 331
and 332. In this case, the selector 336 can be omitted.
[0067] FIG. 9 is a circuit block diagram showing another example of
the circuit configuration of the backlight unit 3. The backlight
unit 3 shown in FIG. 9 has one constant current source 321 and two
LED strings S11 and S12. In the circuit configuration shown in FIG.
9, the two LED strings S11 and S12 are connected in parallel with
one constant current source 321. However, the number of LED strings
to be connected in parallel is not necessarily limited to two and
can be three or more. Further, the circuit configuration shown in
FIG. 9 has one constant current source 321. However, the number of
constant current sources does not have to be one and can be two or
more.
[0068] In the circuit configuration shown in FIG. 9, the current
regulator 33 includes the differential amplifier circuit 331 and
332, the reference voltage generating circuit 335, the field-effect
transistors 33A and 33B, and the current sensing resistors R11 and
R12. The light emission controller 34 includes the switch
controller 341 and the transistors Q341 and Q342. Note that the LED
strings S11 and S12 are disposed in a manner shown in FIG. 6. In
other words, the LED string S11 is disposed in the upper part of
the liquid crystal display panel 2, whereas the LED string S12 is
disposed in the lower part of the liquid crystal display panel
2.
[0069] Here, suppose that a left-eye image signal and a right-eye
image signal are input to the signal processor 1 as the input image
signals in FIG. 1. The signal processor 1 converts these 60-Hz
input image signals into a 120-Hz left-eye image signal and a
120-Hz right-eye image signal, and outputs the resultant signals to
the liquid crystal display panel 2. In synchronization with
outputting the left-eye and right-eye image signals, the signal
processor 1 outputs a control signal to the backlight unit 3. As a
result, a stereoscopically perceivable image is displayed on the
liquid crystal display panel 2.
[0070] FIG. 10 is a timing chart showing an example of operations
by the LED strings in the configuration shown in FIG. 9. Section
(A) of FIG. 10 shows a left-eye period for displaying an image
based on the left-eye image signal and a right-eye period for
displaying an image based on the right-eye image signal. Section
(B) of FIG. 10 shows write operations for writing on the pixels of
the liquid crystal display panel 2. During the left-eye period, the
write operation is executed based on the left-eye image signal that
is input from the signal processor 1. During the right-eye period,
the write operation is executed based on the right-eye image signal
that is input from the signal processor 1. Section (C) of FIG. 10
shows an on-off operation of the backlight unit 3. The backlight
unit 3 is turned on, during a period between when the write
operations are completed and when the subsequent write operations
are started. Sections (D) and (E) of FIG. 10 show current flowing
when the LED strings S11 and S12 connected in parallel with the
constant current source are alternately turned on. Specifically,
Section (D) shows current flowing in the LED string S11, and
Section (E) shows current flowing in the LED string 512. Section
(F) of FIG. 10 shows currents flowing in the LED strings S11 and
S12 when the LED strings S11 and S12 are connected in parallel with
the constant current source and are simultaneously turned on.
[0071] Note that the LED strings S11 and S12 are disposed in a
manner shown in FIG. 6. In other words, the LED string S11 is
disposed in the upper part of the liquid crystal display panel 2,
and the LED string S12 is disposed in the lower part of the liquid
crystal display panel 2. When the LED strings S11 and S12 that are
connected in parallel with the constant current source are turned
on simultaneously, and when the constant current source has a rated
current of 120 mA, for example, current of 60 mA flows in the LED
strings S11 and S12, as shown in Section (F) of FIG. 10. At this
time, a duty of backlights for left-eye or right-eye is 25% per
frame cycle. In addition, a peak current Ip-p is 60 mA. Therefore,
an effective current is 60 mA.times.(0.25).sup.1/2=30 mArms.
[0072] On the other hand, when the LED strings S11 and S12 are
connected in parallel as shown in FIG. 9 and are turned on
individually, current of 120 mA is supplied to each of the LED
strings S11 and S12 during a period in which the duty is 25%/2.
Thus, the effective current is 120 mA.times.(0.25/2).sup.1/2=42.4
mArms. As a result, the light quantity of the LED strings S11 and
S12 can be increased, resulting in an increase in the brightness of
the backlight unit 3.
[0073] The circuit configuration of the backlight unit 3 is not
limited to the examples shown in FIGS. 2, 5, and 9. Additional
examples of the circuit configuration of the backlight unit 3 are
described with reference to FIGS. 11 to 16.
[0074] FIG. 11 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit 3
according to the present implementation. The backlight unit 3 shown
in FIG. 11 has one constant current source 321 and two LED strings
S11 and S12. In the circuit configuration shown in FIG. 11, two LED
strings S11 and S12 are connected in parallel with one constant
current source 321. However, the number of LED strings to be
connected in parallel is not limited to two and can be three or
more LED strings. In addition, the circuit configuration shown in
FIG. 11 has one constant current source 321. However, the number of
constant current sources does not have to be one and can be two or
more. The same is true for the examples shown in FIGS. 12 to 16,
which are described hereinafter.
[0075] In the circuit configuration shown in FIG. 11, the current
regulator 33 includes the differential amplifier circuits 331 and
332, the reference voltage generating circuit 335, and variable
resistors R31 and R32.
[0076] In the example of the circuit configuration shown in FIG.
11, the variable resistor R31 is connected in series between the
LED string S11 and the constant current source 321. The variable
resistor R32 is connected in series between the LED string S12 and
the constant current source 322. The differential amplifier circuit
331 controls a resistance value of the variable resistor R31 in
accordance with a detection voltage Vr31 of the variable resistor
R31 and the reference voltage Vref. The differential amplifier
circuit 332 controls a resistance value of the variable resistor
R32 in accordance with a detection voltage Vr32 of the variable
resistor R32 and the reference voltage Vref.
[0077] In the circuit configuration shown in FIG. 11, currents
flowing in the LED strings S11 and S12 can be equalized. Note that
the variable resistors R31 and R32 can be configured by, for
example, field-effect transistors. In other words, increasing the
gate voltages of the field-effect transistors can reduce
on-resistances of the field-effect transistors, and on the other
hand, reducing the gate voltages can increase the
on-resistances.
[0078] FIG. 12 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit 3. In
the circuit configuration shown in FIG. 12, the current regulator
33 includes the field-effect transistors 33A and 33B, and current
sensing resistors R11 and R12. The gate of the field-effect
transistor 33A is connected to the connection point between the
resistor R12 and the field-effect transistor 33B. The gate of the
field-effect transistor 33B is connected to the connection point
between the resistor R11 and the field-effect transistor 33A.
[0079] In the circuit configuration shown in FIG. 12, the current
flowing in the other LED string is used for reference. When the
current flowing in the LED string S12 increases, the detection
voltage Vr12 of the current sensing resistor R12 rises, increasing
the gate voltage of the field-effect transistor 33A. Therefore, the
current flowing in the field-effect transistor 33A, which is the
current flowing in the LED string S11, can be increased. On the
other hand, when the current flowing in the LED string S12
decreases, the detection voltage Vr12 of the current sensing
resistor R12 drops, decreasing the gate voltage of the field-effect
transistor 33A. Therefore, the current flowing in the field-effect
transistor 33A, which is the current flowing in the LED string S11,
can be reduced.
[0080] Similarly, when the current flowing in the LED string S11
increases, the detection voltage Vr11 of the current sensing
resistor R11 rises, increasing the gate voltage of the field-effect
transistor 33B. Therefore, the current flowing in the field-effect
transistor 33B, which is the current flowing in the LED string S12,
can be increased. On the other hand, when the current flowing in
the LED string S11 decreases, the detection voltage Vr11 of the
current sensing resistor R11 drops, decreasing the gate voltage of
the field-effect transistor 33B. Therefore, the current flowing in
the field-effect transistor 33B, which is the current flowing in
the LED string S12, can be reduced. As a result, currents flowing
in the LED strings S11 and S12 can be equalized also in the circuit
configuration shown in FIG. 12.
[0081] FIG. 13 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit 3. In
the circuit configuration shown in FIG. 13, amplifier circuits 33E
and 33F are added to the circuit configuration shown in FIG. 12. In
other words, the gate of the field-effect transistor 33A is
connected to the connection point between the resistor R12 and the
field-effect transistor 33B via the amplifier circuit 33E. The gate
of the field-effect transistor 33B is connected to the connection
point between the resistor R11 and the field-effect transistor 33A
via the amplifier circuit 33F. In the circuit configuration shown
in FIG. 13, the current regulator 33 includes the amplifier
circuits 33E and 33F, the field-effect transistors 33A and 33B, and
the current sensing resistors R11 and R12.
[0082] The amplifier circuit 33E applies a voltage obtained by
amplifying the detection voltage Vr12 of the resistor R12, to the
gate of the field-effect transistor 33A. The amplifier circuit 33F
applies a voltage obtained by amplifying the detection voltage Vr11
of the resistor R11, to the gate of the field-effect transistor
33B. Because the circuit configuration shown in FIG. 13 operates in
the same manner as the circuit configuration shown in FIG. 12,
currents flowing in the LED strings S11 and S12 can be
equalized.
[0083] FIG. 14 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit 3. In
the circuit configuration shown in FIG. 14, neither the
differential amplifier circuits nor the reference voltage
generating circuit is provided, and variable resistors are
connected in place of the field-effect transistors and current
sensing resistors. In other words, a variable resistor R31 is
connected in series between the LED string S11 and the constant
current source 321, while a variable resistor R32 is connected in
series between the LED string S12 and the constant current source
322. In the circuit configuration shown in FIG. 14, the current
regulator 33 includes the variable resistors R31 and R32.
[0084] In the circuit configuration shown in FIG. 14, the current
flowing in the other LED string is used for reference. The
resistance values of the variable resistors R31 and R32 are
controlled based on the detection voltages Vr32 and Vr31 of the
variable resistors R32 and R31, respectively. In other words, when
the detection voltage Vr32 rises, the resistance value of the
variable resistor R31 is reduced. When the detection voltage Vr32
drops, the resistance value of the variable resistor R31 increases.
When the detection voltage Vr31 rises, the resistance value of the
variable resistor R32 drops. When the detection voltage Vr31 drops,
the resistance value of the variable resistor R32 increases.
Therefore, in the circuit configuration shown in FIG. 14 because
the resistance values of the variable resistors R31 and R32 are
controlled in the same manner as the resistance values of the
variable resistors R31 and R32 shown in FIG. 11, currents flowing
in the LED strings S11 and S12 can be equalized.
[0085] FIG. 15 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit 3. In
the circuit configuration shown in FIG. 15, amplifier circuits 33E
and 33F are added to the circuit configuration shown in FIG. 14. In
other words, the resistance value of the variable resistor R31 is
controlled by the amplified voltage of the detection voltage Vr32
of the variable resistor R32 amplified by the amplifier circuit
33F. The resistance value of the variable resistor R32 is
controlled by the amplified voltage of the detection voltage Vr31
of the variable resistor R31 amplified by the amplifier circuit
33E. In the circuit configuration shown in FIG. 15, the current
regulator 33 includes the amplifier circuits 33E and 33F and the
variable resistors R31 and R32. The circuit configuration shown in
FIG. 15 is exactly the same as that shown in FIG. 14, except that
the circuit configuration shown in FIG. 15 has the amplifier
circuits 33E and 33F. Thus, as with the circuit configuration shown
in FIG. 14, currents flowing in the LED strings S11 and S12 can be
equalized also in the circuit configuration shown in FIG. 15.
[0086] FIG. 16 is a circuit block diagram showing yet another
example of the circuit configuration of the backlight unit 3. The
circuit configuration shown in FIG. 16 has voltage-PWM conversion
circuits 338 and 339 in place of the differential amplifier
circuits. The rest of the configuration of the circuit
configuration shown in FIG. 16 is same as that of the circuit
configuration shown in FIG. 9.
[0087] In the circuit configuration shown in FIG. 16, the current
regulator 33 includes the voltage-PWM conversion circuits 338 and
339, the reference voltage generating circuit 335, the field-effect
transistors 33A and 33B, and the current sensing resistors R11 and
R12. The light emission controller 34 includes the switch
controller 341 and the transistors Q341 and Q342.
[0088] The voltage-PWM conversion circuit 338 outputs a PWM signal
to the gate of the field-effect transistor 33A so that the
detection voltage Vr11 of the current sensing resistor R11 becomes
equal to the reference voltage Vref. In other words, when the Vr11
is greater than the Vref, the voltage-PWM conversion circuit 338
outputs a PWM signal that drops the gate voltage of the
field-effect transistor 33A. When, on the other hand, the Vr11 is
lower than the Vref, the voltage-PWM conversion circuit 338 outputs
a PWM signal that increases the gate voltage of the field-effect
transistor 33A. The voltage-PWM conversion circuit 339 operates in
the same manner as the voltage-PWM conversion circuit 338.
Therefore, the voltage-PWM conversion circuits 338 and 339 control
the field-effect transistors 33A and 33B so that the detection
voltages Vr11 and Vr12 of the current sensing resistors R11 and R12
become equal to each other as follows: Vref=Vr11=Vr12. As a result,
currents flowing in the LED strings S11 and S12 become equal to
each other. Therefore, the circuit configuration shown in FIG. 16
can also prevent or reduce the variations in the light quantity of
each light-emitting diode L11 and the like.
[0089] In the implementation described above, the number of
light-emitting diodes included in the LED strings S11 and the like
is set as, for example, M=10; however, M may be one or more. Even
when M=1, variations in the light quantity of one light-emitting
diode configuring the LED string S11 and the light quantity of one
light-emitting diode configuring the LED string S12 can be
prevented or reduced.
[0090] The implementation described above mainly includes
inventions having the following configurations.
[0091] The display apparatus of the instant application has several
advantages. In one aspect, even when there are fluctuations in the
forward voltages of the light-emitting diodes and the forward
voltages of the light-emitting diode strings are different from
each other, since each current flowing in each of the
light-emitting diode strings may be regulated by the current
regulator, the variations in the light quantity of the
light-emitting diodes configuring the light-emitting diode strings
may be prevented or reduced, without increasing the labor and
costs. Moreover, because the drive unit is connected in series with
the group of light-emitting diode strings in which the N
light-emitting diode strings are connected in parallel with each
other, the number of drive units may be reduced to 1/N, as compared
to the configuration in which the drive units are respectively
connected in series with the light-emitting diode strings. Thus, a
simple configuration can be achieved.
[0092] In another aspect, by controlling the current regulating
element based on the reference voltage and the detection voltage,
it may be possible to regulate each current flowing in the resistor
element, that is, each current flowing in each of the
light-emitting diode strings connected in series with the resistor
element. As a result, it may be possible to prevent or reduce the
variations in the light quantity of the light-emitting diodes
included in the light-emitting diode strings. In addition, the
current regulator element is connected in series with the drive
unit. Hence, it may be possible to increase the withstand voltage
of the drive unit by the level of the withstand voltage of the
current regulating element.
[0093] In another aspect, by controlling the transistor by the
voltages generated by the amplifier circuit, it may be possible to
favorably regulate each current flowing in each of the
light-emitting diode strings. As a result, it may be possible to
prevent or reduce the variations in the light quantity of the
light-emitting diodes included in each of the light-emitting diode
strings. In addition, the transistor is connected in series with
the drive unit. Hence, it may be possible to increase the withstand
voltage of the drive unit by the level of the withstand voltage of
the transistor.
[0094] In another aspect, because the amplifier circuit of the
backlight device may be a differential amplifier circuit, each
amplifier circuit can be configured more simply than an ordinary
amplifier circuit.
[0095] In another aspect, by controlling a transistor by means of
the PWM signal output by a PWM circuit, the display apparatus of
the instant application may be able to favorably regulate each
current flowing in each of the light-emitting diode strings. As a
result, it may be possible to prevent the variations in the light
quantity of the light-emitting diodes configuring each of the
light-emitting diode strings. In addition, the transistor is
connected in series with the drive unit. Hence, it may be possible
to increase the withstand voltage of the drive unit by the level of
the withstand voltage of the transistor. The transistor of the
display apparatus may include a field-effect transistor. Therefore,
almost no current flows to the gate thereof, and hence, it may be
possible to reduce current loss.
[0096] In another aspect, the display apparatus of the instant
application may prevent or reduce the variations in the light
quantity of each of the light-emitting diodes which configure each
of the light-emitting diode strings to which current is
supplied.
[0097] Generally, the drive unit may supply current within the
range of a rated current. Therefore, when the drive unit with the
same rated current is used, more current can be supplied when
simultaneously supplying current to one or each of the K
light-emitting diode strings out of the N light-emitting diode
strings, compared to when simultaneously supplying current to each
of the N light-emitting diode strings that are connected in
parallel. As a result, by supplying more current to the
light-emitting diode strings using the drive unit with the same
rated current, the light quantity of the light-emitting diodes can
be increased, without having the costs of the drive unit increased.
Thus, the display panel can be illuminated at higher intensity.
[0098] The light emission controller of the display apparatus may
perform a control so that the current is supplied from the drive
unit to each of the N light-emitting diode strings sequentially and
one by one, and the current regulator may regulate each current
that is supplied to each of the N light-emitting diode strings
sequentially and one by one by the light emission controller.
According to this configuration, it may be possible to cause the N
light-emitting diode strings to emit light with the same light
quantity one by one, without causing variations in the light
quantity of each of the light-emitting diodes which configure each
of the light-emitting diode strings to which current is
supplied.
[0099] In another aspect, the light emission controller of the
display apparatus may perform a control so that the current is
supplied from the drive unit to the one or each of the K
light-emitting diode strings every predetermined period, and the
current regulator may regulate each current supplied to the one or
each of the K light-emitting diode strings every predetermined
period by the light emission controller. According to this
configuration, it may be possible to cause the one or each of the K
light-emitting diode strings to emit light with the same light
quantity one by one, without causing variations in the light
quantity of each of the light-emitting diodes which configure each
of the light-emitting diode strings to which current is
supplied.
[0100] In another aspect, the instant application describes a
display apparatus in which N light-emitting diode strings
illuminate different regions of the display panel. The N
light-emitting diode strings include a first light-emitting diode
string and a second light-emitting diode string that illuminate the
regions adjacent to each other. The light emission controller may
perform control so that current may be supplied from the drive unit
to only the first light-emitting diode string during a first
period, that current may be supplied from the drive unit to each of
the first and second light-emitting diode strings during a second
period subsequent to the first period, and that current is supplied
from the drive unit to only the second light-emitting diode string
during a third period subsequent to the second period. Therefore,
by regulating each current flowing in each of the light-emitting
diode strings by the current regulator, it may be possible to
alternately and smoothly illuminate, at uniform intensity, the
regions of the display panel that are adjacent to each other.
[0101] In yet another aspect, each current flowing in each of the N
light-emitting diode strings that are connected in parallel with
each other may be regulated. Therefore, even when there are
fluctuations in the forward voltages of the light-emitting diodes,
and the forward voltages of the entire light-emitting diode strings
may be different from each other, it may be possible to prevent
variations in the light quantity of the respective light-emitting
diodes configuring the light-emitting diode strings.
[0102] The display apparatus of the instant application may be
useful as a display apparatus capable of reducing fluctuations in
brightness that are caused due to the individual difference in the
respective light-emitting diode elements.
[0103] While the foregoing has described what are considered to be
the best mode and/or other examples, it is understood that various
modifications may be made therein and that the subject matter
disclosed herein may be implemented in various forms and examples,
and that they may be applied in numerous applications, only some of
which have been described herein. It is intended by the following
claims to claim any and all modifications and variations that fall
within the true scope of the present teachings.
* * * * *